1. Field of the Invention
The present invention relates to an electromagnetic flow meter configured to measure a flow rate of a fluid. More specifically, the present invention relates to a technique to apply a resin lining on an inner surface of a measurement pipe in which a measurement target fluid is to flow.
2. Description of the Related Art
An electromagnetic flow meter is configured to measure a flow rate by applying an electric current to a coil to generate a magnetic field inside a measurement pipe, and by detecting magnitude of an electromotive force generated in proportion to the electric conductivity of a liquid flowing inside the measurement pipe. Generally, a resin lining made of fluororesin, polyurethane resin or the like is applied on an inner surface of the measurement pipe of the above-described electromagnetic flow meter in order to prevent embrittlement.
Transfer molding is known as a method for applying a resin lining in an electromagnetic flow meter. This method involves the following steps: fitting molds to both ends and the inside of a measurement pipe; heating these molds up to a temperature close to a melting point of resin used for lining; and pressurizing melted resin to feed the resin into clearances between the measurement pipe and the molds.
In another method for applying a resin lining, the method involves the following steps: fitting molds to both ends and the inside of a measurement pipe; and pressurizing melted resin without heating the resin to feed the resin into clearances between the measurement pipe and the molds.
Further, in another method for applying a resin lining, the method involves the following steps: fitting molds to both ends and the inside of a measurement pipe; putting resin pellets used for lining into clearances between the measurement pipe and the molds in advance; heating the resin pellets until the pellets are melted in the clearances between the measurement pipe and the molds; and thereafter, pressurizing and molding the resin by clipping the molds with a press machine or the like.
Regarding the conventional electromagnetic flow meter including the measurement pipe to which the resin lining is applied, there is known a technique for preventing the resin lining from being detached from the measurement pipe. This technique forms the lining by feeding the resin after attaching a cylindrical porous plate serving as a reinforcing member onto the inner surface of the measurement pipe.
Japanese Examined Patent Application Publication No. 03-124 (Patent Document 1) discloses a forming method of pipe lining for an electromagnetic flow meter. According to this method, a porous plate is used as a reinforcing member buried in resin. The porous plate is firstly wound cylindrically so as to be inserted into a measurement pipe, thereby forming a porous pipe body. Next, a spacer is fitted to an outer peripheral surface of this porous pipe body. The porous pipe body provided with the spacer is then inserted into the measurement pipe and fixed thereto. Then, the measurement pipe body is coated with resin by insertion molding. In this method, before the porous pipe body is coated with resin, the two end edges in a circumferential direction of the porous pipe body are shifted relatively to each other in an axial direction to expand the diameter of the porous pipe body, while being in close contact with each other, until an outer peripheral surface of the spacer comes in close contact with an inner peripheral surface of the measurement pipe.
Japanese Examined Utility Model Application Publication No. 02-39214 (Patent Document 2) discloses an electromagnetic flow meter including a lining that is applied on an inner surface of a conducting pipe by means of insertion molding. This electromagnetic flow meter includes: a cylinder provided with a fastener which is fixed to the inner surface of the conducting pipe and which is configured to establish fastening integrally with the lining; a reinforcing member provided with through holes formed at least along a seam of the cylinder; and a lining fastener which is provided on the conductive pipe to face the though holes and which is configured to prevent detachment of the lining.
Japanese Examined Utility Model Application Publication No. 61-16493 (Patent Document 3) discloses a technique to prevent detachment of a resin lining from a measurement pipe without using a reinforcing member. According to this technique, dovetail grooves are formed on an inner surface of the measurement pipe either in a circumferential direction or in an axial direction, and the lining is formed by feeding resin thereafter.